This invention relates to improvements in apparatus and methods for operating sailboats.
In one aspect, the invention concerns apparatus for measuring the horizontal angle between the tangent to the luff of the sail and the direction of the apparent wind.
In another respect, the invention concerns a method for adjusting the angular position of a sail to provide maximum pulling power.
On a close-hauled or reaching course, the sails of a sailboat operate as vertical airfoils to produce motive force to move the boat through the water. As the sail moves through the apparent wind, the increased velocity of flow of air on the lee or convex side of the sail causes the formation of a low-pressure field on the lee side of the sail. This low-pressure area is not only the source of the negative or suction power acting on the sail, it also sets up an important aerodynamic chain reaction which leads to the forming of an even greater pressure differentiation between the lee and windward sides of the sail. As the leading edge (luff) of the sail approaches "new" air, the air mass must be split and, when it does, more of this air mass is attracted to the low-pressure area on the lee side of the sail. Thus, an even greater mass of air must travel faster around the lee side of the sail which results in an even greater decrease in pressure which, in turn, attracts even more of the air mass. This chain reaction continues to build until maximum flow velocity for the existing wind condition is reached, and a maximum low-pressure area is created on the lee side of the sail.
Since the length of the path by which the air must move past the sail varies with the angle of attack of the sail to the apparent wind, it is obvious and well known in the art that adjustments in the angular position of the sail would increase or decrease the motive power produced by the sail. The increase or decrease in the speed of the boat in response to large changes in the angular position of sails is easily noticed, even by the novice sailor. However, where even very minute changes in boat speed, not otherwise noticeable, are important as in sailboat racing, it is very difficult, even for the most experienced sailor, to precisely adjust the angular position of the sail to achieve maximum "pulling" power.
In the past, several devices have been provided to assist the sailor in finding and maintaining the optimum angle of attack for his sails. Crude devices such as pieces of string or cloth have been attached to the standing rigging of the boat as a means for visually indicating the direction of the apparent wind. Similarly, wind vanes have been attached at various points on the boat such as at the mast head, on the spreaders, on the deck, or on the mast itself. All of these devices serve to provide a visual indication of the angle of the apparent wind to the center line of the boat. To utilize such devices, the sailor must first determine the angle between the apparent wind and the center line of the boat by observing the telltale or the wind vane and must then make a second correlation between the center line of the boat and the angular position of the sail. While these correlations become almost instinctive, they do require both time and relatively unrestricted visibility of the apparent wind direction indicating device. Under some sailing conditions and especially under racing conditions, the sailor has only very limited time and in some cases restricted visibility and, consequently, he is unable to always maintain the angle of attack of his sails at the optimum angle for maximum pulling power, especially in shifting winds or with changes in boat speed, both of which cause changes in the angle of the apparent wind.
It would therefore be highly desirable to provide a device of simplified construction and operation which can be quickly and conveniently placed in direct line of observation by the helmsman and which gives a direct indication of the angle of attack of the sail.
It would also be highly advantageous to provide a method for adjusting the angular position of the sail by using the direct indication provided to adjust the sail angle to produce maximum pulling power.
Accordingly, it is the principal object of the present invention to provide improved apparatus for indicating the angle of attack of a sail.
Another principal object of the invention is to provide a method of adjusting the angular position of the sail to produce the maximum pulling power.
These and other, further and more specific objects and advantages of the invention will be apparent to those skilled in the art from the following detailed description thereof, taken in conjunction with the drawings, in which: